Pelagic Organisms in Scottish Lakes. 53 



in the shallow waters of the east and south, but occurs here 

 and there in the Highlands, as in Loch Ness, where, however, 

 it is a littoral form. Dr Scott has recorded it from a con- 

 siderable number of lochs in the north and west, the 

 Shetland Islands, Uist, and Barra. Mr J. Hewitt has 

 also recently noted it from a number of lochs in Lewis. 

 I have not in a single instance found the species in the 

 plankton of the lochs in those districts. I consider it 

 probable that, as Dr Scott in many instances made his 

 examination from the shore, while we invariably worked 

 from boats, it will be found that where B. longirostris occurs 

 it will be a littoral species, while B. oitusirostris, as in 

 Loch Ness, is the true pelagic form. 



Baphnia liyalina, Leydig, var. lacustris, varying to var. 

 galeata, is common over nearly the whole of Scotland. I 

 think it probable that in parts of the lowlands of the east 

 and north it is replaced by B. cucullata, Sars, but the dis- 

 tribution of the latter species has not yet been worked out. 



The distribution of all the species of Biaptomus is of the 

 greatest interest. Four species are common in the plankton 

 of the whole or some part of the country, — these are 

 B. gracilis, B. laciniatus, B. laticeps, and B. toierzejskii ; 

 there is a single record of another species, B. haccilifcr, 

 which was found in Loch Earn ; B. castor is found only 

 in small ponds, and is rare, though widely distributed. 



Biaptomus gracilis, G. 0. Sars, is found in almost every 

 loch on the mainland, is very rare in Orkney, and appears 

 to be absent from the Shetland Islands, Uist, and Barra. 

 Mr Hewitt tells me that it is frequent in Lewis. It has been 

 found at a greater altitude than any of the other species, 

 being the only species in most of the highest lochs surveyed. 



Biaptomus laciiiiatus, Lilljeb., is commoner in Lewis than 

 elsewhere ; is frequent in Sutherland, Boss, and Inverness ; 

 occurs in Loch Shiel, Loch Lomond, and Loch Doon ; and 

 has its eastern limit, so far as known, in som small lochs 

 in the extreme west of Aberdeenshire, where it was found 

 by Mr B. M. Clark (3). It is more alpine than the two 

 following species, and in some districts, as in the neighbour- 

 hood of the Great Glen, for instance, it occupies the hill 



